179289f0bf
### What changes were proposed in this pull request?
This PR intends to clean up the SQL documents in `doc/sql-ref*`.
Main changes are as follows;
- Fixes wrong syntaxes and capitalize sub-titles
- Adds some DDL queries in `Examples` so that users can run examples there
- Makes query output in `Examples` follows the `Dataset.showString` (right-aligned) format
- Adds/Removes spaces, Indents, or blank lines to follow the format below;
```
---
license...
---
### Description
Writes what's the syntax is.
### Syntax
{% highlight sql %}
SELECT...
WHERE... // 4 indents after the second line
...
{% endhighlight %}
### Parameters
<dl>
<dt><code><em>Param Name</em></code></dt>
<dd>
Param Description
</dd>
...
</dl>
### Examples
{% highlight sql %}
-- It is better that users are able to execute example queries here.
-- So, we prepare test data in the first section if possible.
CREATE TABLE t (key STRING, value DOUBLE);
INSERT INTO t VALUES
('a', 1.0), ('a', 2.0), ('b', 3.0), ('c', 4.0);
-- query output has 2 indents and it follows the `Dataset.showString`
-- format (right-aligned).
SELECT * FROM t;
+---+-----+
|key|value|
+---+-----+
| a| 1.0|
| a| 2.0|
| b| 3.0|
| c| 4.0|
+---+-----+
-- Query statements after the second line have 4 indents.
SELECT key, SUM(value)
FROM t
GROUP BY key;
+---+----------+
|key|sum(value)|
+---+----------+
| c| 4.0|
| b| 3.0|
| a| 3.0|
+---+----------+
...
{% endhighlight %}
### Related Statements
* [XXX](xxx.html)
* ...
```
### Why are the changes needed?
The most changes of this PR are pretty minor, but I think the consistent formats/rules to write documents are important for long-term maintenance in our community
### Does this PR introduce any user-facing change?
Yes.
### How was this patch tested?
Manually checked.
Closes #28151 from maropu/MakeRightAligned.
Authored-by: Takeshi Yamamuro <yamamuro@apache.org>
Signed-off-by: Sean Owen <srowen@gmail.com>
3.8 KiB
| layout | title | displayTitle | license |
|---|---|---|---|
| global | DESCRIBE QUERY | DESCRIBE QUERY | Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. |
Description
The DESCRIBE QUERY statement is used to return the metadata of output
of a query. A shorthand DESC may be used instead of DESCRIBE to
describe the query output.
Syntax
{% highlight sql %} { DESC | DESCRIBE } [ QUERY ] input_statement {% endhighlight %}
Parameters
QUERY- This clause is optional and may be omitted.
input_statement-
Specifies a result set producing statement and may be one of the following:
- a
SELECTstatement - a
CTE(Common table expression)statement - an
INLINE TABLEstatement - a
TABLEstatement - a
FROMstatement
- a
Examples
{% highlight sql %}
-- Create table person
CREATE TABLE person (name STRING , age INT COMMENT 'Age column', address STRING);
-- Returns column metadata information for a simple select query DESCRIBE QUERY select age, sum(age) FROM person GROUP BY age; +--------+---------+----------+ |col_name|data_type| comment| +--------+---------+----------+ | age| int|Age column| |sum(age)| bigint| null| +--------+---------+----------+
-- Returns column metadata information for common table expression (CTE).
DESCRIBE QUERY WITH all_names_cte
AS (SELECT name from person) SELECT * FROM all_names_cte;
+--------+---------+-------+
|col_name|data_type|comment|
+--------+---------+-------+
| name| string| null|
+--------+---------+-------+
-- Returns column metadata information for a inline table. DESC QUERY VALUES(100, 'John', 10000.20D) AS employee(id, name, salary); +--------+---------+-------+ |col_name|data_type|comment| +--------+---------+-------+ | id| int| null| | name| string| null| | salary| double| null| +--------+---------+-------+
-- Returns column metadata information for TABLE statement.
DESC QUERY TABLE person;
+--------+---------+----------+
|col_name|data_type| comment|
+--------+---------+----------+
| name| string| null|
| age| int| Agecolumn|
| address| string| null|
+--------+---------+----------+
-- Returns column metadata information for a FROM statement.
-- QUERY clause is optional and can be omitted.
DESCRIBE FROM person SELECT age;
+--------+---------+----------+
|col_name|data_type| comment|
+--------+---------+----------+
| age| int| Agecolumn|
+--------+---------+----------+
{% endhighlight %}